Additive manufacturing, also known as 3D printing, is any of various processes used to make a three-dimensional object. With 3D printing, additive processes are used, in which successive layers of material are laid down under computer control. A 3D printed object is typically created through sequential construction of thin layers (i.e., slices) following a digital model. Stereolithography (SL) is one particular type of additive manufacturing wherein a liquid polymer resin is hardened by selective exposure to radiation to form a thin layer. The shape of the hardened thin layer is defined by the pattern of a subject slice of the digital model. The energy source of radiation can be in the form of electromagnetic waves or electron beam. The common energy source is ultraviolet, visible or infrared radiation. The liquid photopolymer resin used to form the 3D object can contain multiple components including monomers, oligomers, photoinitiators, blockers, colorants and other additives.
One challenge encountered with SL is the presence of uncured or partially-cured resin on the surfaces of the printed 3D object. Uncured resin must be removed and partially-cured resins render the object tacky and difficult to clean. Because most of the current resin formulations apply monomers or oligomers that are soluble only in certain organic solvents, the 3D printed objects need to be washed by rinsing or utilization of ultrasonication with organic solvents, such as isopropanol or acetone. The organic solvents are often volatile organic chemicals (VOCs) which are regulated by the Environmental Protection Agency (EPA) and Occupational Safety and Health Administration (OSHA). The use of organic solvents has several disadvantages: first, the organic solvents are flammable and harmful to the human body and environment making them less than ideal chemicals for use by ordinary users of 3D printing systems having little or no knowledge of chemistry; second, the storage and disposal of organic solvents can be challenging; and third, organic solvents add costs to printing the 3D objects.
Another challenge encountered with SL is shrinkage. Polymerization shrinkage happens during hardening of the liquid photopolymer resin. The shrinkage during SL, 3D printing can result in printing inaccuracies, such as shrunken size or even warped objects, as well as a high probability of failed printing, such as detachment between two adjacent thin layers. It is well known that polymerization shrinkage is due to the space reduction related to van der Waals spaces being substituted by chemical covalent bond spaces where monomer/oligomer molecules are converted into a polymer network.
It would be advantageous to develop a water-washable resin formulation which overcomes the drawbacks noted herein as well as improving 3D printing systems and methods.